Date: Mon, 7 May 2001 21:25:23 +0300 (EEST) From: Pekka Savola <pekkas@netcore.fi> To: Steve Watt <steve@Watt.COM> Cc: <stable@freebsd.org> Subject: Re: 4.3-S: No buffer space available [SOLVED: dummynet] Message-ID: <Pine.LNX.4.33.0105072113420.27233-100000@netcore.fi> In-Reply-To: <200105071807.f47I7u731297@wattres.Watt.COM>
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On Mon, 7 May 2001, Steve Watt wrote: > pekkas@netcore.fi wrote: > >On Sat, 5 May 2001, Pekka Savola wrote: > >Ok. This was caused by the dummynet rule, either directly or indirectly. > > [...] > > >The traffic being shaped to 20Mbit/s ranged from 25-35 Mbit/s (steady), > >mostly outgoing. > > >Has dummynet been tested in this kind of heavy environment? > > > >Is there a better value for 'queue', e.g. 1000Kbytes in this scenario? > > OK, this seems to me to be a guaranteed cause of "no buffer space > available". If your pipe is only 20Mb and you're trying to stuff > 25-35Mb though it, that's 5-15Mb that need to be stashed somewhere > *every second*. A perfectly good place to stash that amount of > stuff is /dev/null, unless you have some *huge* buffers allocated. > > Am I missing something? > > I don't know if dummynet supports it, but if you can enable random > early dropping[1] (RED), that should do a decent job of throttling > TCP connections to lower the demand. I don't try to stuff 25-35 Mb/s through it exactly; that's what the traffic would be if there was no shaping at all. The point with this kind of traffic shaping is that packets need not necessarily be thrown away that much. If you let a packet here and there be dropped from a TCP connection, the protocol will automatically decrease the window size. The protocol algorithm will learn the optimal speed for the connection. Actual packet drop rate is well below 1%, which is something that could be buffered (with small delays) too. Not sure how dummynet does this. It also supports RED, but it's a bit heavier to set up. -- Pekka Savola "Tell me of difficulties surmounted, Netcore Oy not those you stumble over and fall" Systems. Networks. Security. -- Robert Jordan: A Crown of Swords To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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